Shift Current in Molecular Crystals Possessing Charge-Transfer Characteristics

Abstract

Further research on organic molecule crystals with spontaneous polarization as a possible candidate for the bulk photovoltaic effect is urgently needed to meet the requirements for optoelectric devices. We demonstrate the shift current in a type of molecular crystal that acts at high temperatures and contains organic molecules with electron donor-acceptor groups, such as paranitroaniline derivatives. We find an extremely strong multicomponent shift-current response along the parallel and perpendicular to polar molecules of the crystals using density-functional simulations, which is more than 10 times larger than the previously reported value for shift current over a broad spectral range from visible to ultraviolet spectrum. Even more intriguing, the remarkable dependency of the conduction- and valence-band dispersions on the lattice constant along polarization allows the shift current in these organic molecule structures to be tuned under stress and doping. Our findings not only suggest a class of organic compounds for realizing the highly controllable shift-current response, but also open up a channel for the search for solar materials.